Section 4.5: GEOLOGY, SOILS, AND...

Section 4.5:

GEOLOGY, SOILS, AND SEISMICITY

EARVIN “MAGIC” JOHNSON RECREATION AREA MASTER PLAN

DRAFT ENVIRONMENTAL IMPACT REPORT

SECTION 4.5 GEOLOGY, SOILS, AND SEISMICITY

Los Angeles County September 2015 Department of Parks and Recreation

4.5-1

4.5 GEOLOGY, SOILS, AND SEISMICITY This section describes the geology, soils, and seismicity setting and potential environmental impacts, as they pertain to implementation of the proposed Project. This section is based on the Draft Geotechnical Evaluation Study (July 2014) for the proposed Project site; refer to Appendix E of this EIR. Information for this section was also obtained from the County of Los Angeles General Plan (1980) and the Los Angeles County Municipal Code.

ENVIRONMENTAL SETTING

SITE HISTORY AND DESCRIPTION

The proposed Project site is located south of E. 120th Street and north of El Segundo Boulevard between S. Avalon Boulevard and Clovis Avenue. Within the existing EMJ Park on the Project site, there are two artificially created lakes, widespread grass lawn areas with scattered trees, paved parking areas, restrooms, soccer fields and typical park amenities including picnic tables, barbecues, drinking fountains and lighting fixtures. Single family residential homes are located in the north-west portion of the site and along eastern portion of the site down S. Central Avenue from E. 120th Street to El Segundo Boulevard. Commercial development is located along the major roads to the west and south of the property. The surface of the site consists of relatively flat ground along the perimeter with gentle hills and mounds located mainly in the central portions. These elevated areas, which range from a few feet to a maximum of about 10 feet in height, are assumed to have been largely created through the placement of soil materials at these locations during excavation and grading that took place to create the two on-site lakes.

Earvin “Magic” Johnson Recreation Area Master Plan Project 4.5 Geology, Soils, and Seismicity

Draft EIR

Los Angeles County September 2015

Department of Parks and Recreation

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A right of way easement (Parcel 6086031273), owned by the County Department of

Water and Power (LACDWP) is also located on the Project site. It presently serves as a

utility corridor for overhead electrical transmission lines.

Non-structural fill soils ranging from less than one foot and up to 10 feet in thickness

cover virtually all of the proposed development area. Because the majority of the fill

soils were not graded to create areas suitable for the construction of structural

improvements, they would require complete removal from all structural and/or

proposed fill areas. A minor-to-moderate amount of approximately two feet of

removals within the native soils present beneath the fill soils may also be required.

REGIONAL GEOLOGIC SETTING

The Project site is located on the Los Angeles coastal plain. This plain is a lowland that

gently slopes seaward, and is underlain by as much as about 30,000 feet of sediments

that rest on granitic and metamorphic basement rocks. The plain is bounded by the

Santa Monica Mountains and San Joaquin Hills to the south, and the Palos Verde Hills

and Pacific Ocean shoreline to the west. The dominant structural feature of this coastal

plain is the northwest trending Newport-Inglewood fault zone.

The nearest known active earthquake fault is the Newport-Inglewood-Rose Canyon

Fault, which is located approximately 0. 7 miles (1.2 kilometers) to the southwest of the

Project site. Other significant faults in the region include the Palos Verdes Fault located

approximately 10 miles (16.1 kilometers) to the southwest; the Los Alamitos Fault

located approximately 9.2 miles (15 kilometers) to the southeast; the Elsinore Fault

located approximately 13.4 miles (21.5 kilometers) to the east; and the Sierra Madre

Fault Zone located approximately 21 miles (33.2 kilometers) to the north.

SITE GEOLOGIC CONDITIONS

The site is underlain by fill soils that were derived mainly from onsite grading while

alluvial sediments are present at depth. Because virtually all of the site has been

modified to some extent in the past, no areas of natural ground remain exposed at the

surface. Existing fill thicknesses across the site range from less than one foot to an


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anticipated maximum thickness of about 10 to 15 feet. The onsite soils consist mainly of

fine-grained clayey sand to sandy clay soils that are soft to very firm and have low

expansion potential.

REGULATORY FRAMEWORK

FEDERAL

No Federal plans, policies, or laws related to geology, soils, or seismicity are applicable

to the proposed Project.

STATE

ALQUIST-PRIOLO EARTHQUAKE FAULT ZONING ACT (1972)

The purpose of the Alquist-Priolo Earthquake Fault Zoning Act is to ensure that no

buildings utilized for human occupancy are constructed on the surface trace of active

faults. Faults are fractures in the earth’s crust where rocks move relative to one another

over time. The Act includes only faults that have ruptured in the last 11,000 years called

active faults. Cities and counties must demonstrate with a geological investigation that

proposed buildings will not be constructed across active faults before a project can be

permitted. If the presence of an active fault is discovered, any structure used for human

occupancy cannot be constructed over the trace of the fault and is required to be set

back from the active fault (generally at least 50 feet).

CALIFORNIA BUILDING CODE (CBC) (2013)

The California Building Code (also known as the California Building Standards Code)

provides a minimum standard to improve safety, sustainability, quality of material, and

maintain consistency for the design and construction of buildings. The code requires

strict building standards specific to California’s unique geologic conditions such as soft

soil and ground shaking from seismic activities.

SEISMIC HAZARDS MAPPING ACT

The purpose of the Seismic Hazards Mapping Act is to address the effects of strong

ground shaking, liquefaction, landslides and other ground failures that occur in the


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State of California induced by earthquakes. The map identifies areas that are prone to

these failures and serves as a guide to minimize the loss of life and property. Seismic

Hazard Zone Maps provide a guidance for mitigation of earthquake-related hazards in

land use planning and the building permit processes.

LOCAL

LOS ANGELES REGIONAL WATER QUALITY CONTROL BOARD

The Los Angeles Regional Water Quality Control Board (LARWQCB) is one of nine

statewide regional water quality boards. The LARWQCB protects ground and surface

water quality in the Los Angeles region, including the coastal watersheds of Los

Angeles and Ventura Counties, along with very small portions of Kern and Santa

Barbara Counties. In order to carry out its mission to preserve and enhance water

quality, the LARWQCB conducts the following range of activities to protect ground and

surface waters under its jurisdictions:

Addresses region-wide and specific water quality concerns through updates of

the Water Quality Control Plan (Basin Plan) for the Los Angeles region;

Prepares, monitors compliance with, and enforces Waste Discharge

Requirements, including NPDES permits;

Implements and enforces local stormwater control efforts;

Regulates the cleanup of contaminated sites, which have already polluted or

have the potential to pollute ground or surface water;

Enforces water quality laws, regulations, and waste discharge requirements;

Coordinates with other public agencies and groups that are concerned with

water quality; and

Informs and involves the public on water quality issues.

CONSTRUCTION STORMWATER PERMITS

Stormwater runoff from construction activity that results in soil disturbances of at least

one acre of total land area (and projects that meet other specific criteria) is governed by


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4.5-5

the State Water Resources Control Board (SWRCB) under Water Quality Order 2009-

0009-DWQ. These regulations prohibit discharges of polluted stormwater from

construction projects that disturb one or more acres of soil.

LOS ANGELES COUNTY GENERAL PLAN

Safety Element

Seismic Hazards

Goal Minimize injury and loss of life, property damage, and the

social, cultural, and economic impacts caused by the

earthquake hazards.

Policy 1 Encourage the use of non-urbanized segments of active fault

zones for rural and open space purposes.

Policy 2 Review projects proposing expansion of existing

development and construction of new development,

especially critical facilities, and encourage them to avoid

localities exposed to high earthquake hazards through such

techniques as cluster development and transfer of

development rights.

Policy 3 Continue enforcement of stringent site investigations (such

as seismic, geological, hydrologic, and soils investigations)

and implementation of adequate hazard mitigation

measures for development projects in areas of high

earthquake hazard, especially those involving critical

facilities. Do not approve proposals and projects which

cannot mitigate safety hazards to the satisfaction of

responsible agencies.

Policy 4 Promote the development of seismically resistant major

lifelines serving Los Angeles County and connecting it to

surrounding regions and the rest of the nation

Policy 5 Promote the strengthening or replacement of critical

facilities; and the retrofitting or abatement of potentially


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hazardous buildings, highway structures, and dams and

reservoirs which do not meet seismic safety standards.

Policy 6 Encourage the preservation and sensitive reuse of historic

buildings that need strengthening for protection from

seismic hazards, in a manner that does not endanger public

safety.

Policy 7 Strengthen earthquake resistance standards for non-

structural components, especially in critical facilities.

Geological Hazards

Goal Protect public safety and minimize the social and economic

impacts from geologic hazards.

Policy 8 Review proposals and projects proposing new development

and expansion of existing development in areas susceptible

to landsliding, debris flow, and rockfalls, and in areas where

collapsible or expansive soils are a significant problem; and

disapprove projects which cannot mitigate these hazards to

the satisfaction of responsible agencies.

Policy 9 Continue to improve and enforce stringent slope

investigation and design standards, and to apply innovative

hazard mitigation and maintenance plans for development

in hillside areas.

Policy 10 Upgrade slope maintenance measures and improve

emergency response capability in hillside areas.

IMPACT ANALYSIS AND MITIGATION MEASURES

METHODOLOGY

An evaluation of the significance of potential impacts related to geology, soils and

seismicity must consider both direct effects as well as indirect effects in the local or

regional context. Potentially significant impacts would generally result if people or

structures are exposed to risk of loss, injury or death from rupture of a known


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4.5-7

earthquake fault or seismic-related ground failure, or location on a geologic unit or soil

that is unstable (including expansive soils), or if the project would result in substantial

soil erosion or the loss of topsoil.

THRESHOLDS OF SIGNIFICANCE

The following thresholds of significance are based, in part on the CEQA Guidelines

Appendix G. For purposes of this EIR, implementation of the proposed Project may

have a significant adverse impact on geology, soils, or seismicity if it would do any of

the following:

Expose people or structures to potential substantial adverse effects, including the

risk of loss, injury, or death involving:

o Rupture of a known earthquake fault, as delineated on the most recent

Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist

for the area or based on other substantial evidence of a known active fault

trace. Refer to Division of Mines and Geology Special Publication 42;

o Strong seismic groundshaking or seismic-related ground failure, including

liquefaction and lateral spreading; or

o Landslides.

Result in substantial soil erosion or the loss of topsoil;

Be located on a geologic unit or soil that is unstable, or that would become

unstable as a result of the project, and potentially result in onsite or offsite

landslide, lateral spreading, subsidence, liquefaction, or collapse;

Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building

Code (1994), creating substantial risks to life or property.


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4.5-8

PROJECT IMPACTS AND MITIGATION

Threshold: Would the Project expose people or structures to potential substantial

adverse effects, including the risk of loss, injury, or death involving:

- Rupture of a known earthquake fault, as delineated on the most recent

Alquist-Priolo Earthquake Fault Zoning Map issued by the State

Geologist for the area or based on other substantial evidence of a known

active fault trace?

- Strong seismic ground shaking?

- Seismic-related ground failure, including liquefaction?

- Landslides?

Impact 4.5-1 Implementation of the Project would not expose people or

structures to potential substantial adverse effects, including the

risk of loss, injury, or death involving rupture of a known

earthquake fault, as delineated on the most recent Alquist-Priolo

Earthquake Fault Zoning Map issued by the State Geologist for

the area or based on other substantial evidence of a known fault;

strong seismic groundshaking; seismic-related ground failure,

including liquefaction; or landslides. This impact would be less

than significant.

The Draft Geotechnical Evaluation Study (July 2014) prepared for the Project found that no

active or potentially active faults are known to exist at the Project’s site and the Project

does not lie within a current State of California Earthquake Fault Zone. The closest

known active fault is the Newport-Inglewood-Rose Canyon Fault located

approximately 0.7 miles southwest of the Project. The historical seismicity of the Project

site entails numerous small-to-medium magnitude earthquake events occurring around

the Project site, predominately associated with the Newport-Inglewood fault. As is the

case with most of California, any future development within the Project site should

anticipate that moderate-to-large seismic events could occur within or in close

proximity to the Project site.


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In addition, the Project site lies on a relatively flat surface. Due to the low relief of the

site and surrounding area, the occurrence of mass movement failures, such as

landslides, rockfalls, or debris flows within such areas is generally not considered

common and no evidence of mass movement was observed on the site. The potential for

liquefaction generally occurs during strong ground shaking within loose, geologic

young, granular sediments where the depth to groundwater is usually less than 50 feet.

The depth to static groundwater within areas of the Project site is approximately 40 feet

below ground surface. However, the site is underlain by relatively dense/stiff deposits

of older alluvium soils and these materials are less susceptible to liquefaction, and is

located outside of areas that may be susceptible to liquefaction. Therefore, the potential

for liquefaction to occur at the site is very low to low. Settlement generally occurs

within areas of loose, granular soils with relatively low density. Since the site is

underlain by relatively dense/stiff, older alluvial materials, the potential for settlement

is considered low. Impacts would be less than significant.

The Draft Geotechnical Evaluation Study (July 2014) has recommended Mitigation

Measures for design and construction of all Project-related facilities in accordance with

the California Building Code. Therefore, implementation of Mitigation Measures GEO-1

through GEO-10 would ensure maximum practicable protection for users of the

buildings and associated infrastructure. All aspects of seismic-related hazards, other

geotechnical hazards, and erosion and sedimentation issues are regulated by the

County and/or the State of California. Impacts would be less than significant.

MM GEO-1 Foundation Support. A compacted fill mat shall be constructed beneath

footings and slabs. The compacted fill mat shall provide a dense, high-

strength soil layer to uniformly distribute the anticipated foundation loads

over the underlying soils. The construction of this compacted fill mat shall

include the removal of any existing non-structural fill material as well as

the removal of any upper, loose/soft to medium dense/stiff underlying

natural earth materials.


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MM GEO-2 General Site Grading. All areas to be graded shall be stripped of

significant vegetation and other deleterious materials. In areas of existing

grass, the grass and upper approximately 3 inches of topsoil must be

removed. The remaining soil, when blended for use as engineered fill, shall

have an organic content of no more than 3 percent.

MM GEO-3 General Site Grading. All existing non-structural fill soils shall be

completely removed from all proposed structural areas. Subsequent to

removal of deleterious items to the satisfaction of the soils engineer, the fill

soils may then be placed as compacted fill. Irrigation and drain lines, as

well as their associated trench backfill materials, shall also be removed

during site clearing and grading.

MM GEO-4 General Site Grading. All existing fills under any proposed flatwork and

paved areas shall be removed and replaced with engineered compacted fill.

MM GEO-5 Preparation of Fill Areas. Prior to placing fill, the surfaces of all areas to

receive fill shall be scarified to a depth of at least 12 inches. The scarified

soil shall be brought to near optimum moisture content and recompacted

to a relative compaction of at least 90 percent.

MM GEO-6 Preparation of Foundation Areas. All footings shall rest upon at least 24

inches of properly compacted fill material. In areas where the required fill

thickness is not accomplished by the recommended removals or by site

rough grading, the footing areas shall be further subexcavated to a depth of

at least 24 inches below the proposed footing base grade, with the

subexcavation extending at least 5 feet beyond the footing lines. Where

removal and/or over-excavation depths exceed 5 feet, subexcavation shall

extend beyond the footing lines a minimum distance equal to the depth of

the removal and/or overexcavation. The bottom of all excavations shall

then be scarified to a depth of at least 12 inches, brought to near optimum

moisture content, and recompacted to at least 90 percent relative


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4.5-11

compaction prior to refilling the excavation to grade as properly

compacted fill. These recommendations are subject to revision pending the

completion of supplemental geotechnical investigation and/or review of

proposed development plans.

MM GEO-7 Engineered Compacted Fill. The onsite soils shall provide adequate quality

fill material, provided they are free from organic matter and other

deleterious materials. Unless approved by the geotechnical engineer, rock

or similar irreducible material with a maximum dimension greater than

12 inches shall not be buried or placed in fills. Rocks or other irreducible

material greater than 12 inches in diameter shall be disposed of within

designated rock disposal areas approved by the soils engineer and/or local

governing agency.

Import fill shall be inorganic, non-expansive granular soils free from rocks

or lumps greater than 6 inches in maximum dimension. Sources for

import fill shall be approved by the geotechnical engineer prior to their

use.

Fill shall be spread in maximum 8-inch uniform, loose lifts, each lift

brought to near optimum moisture content, and compacted to a relative

compaction of at least 90 percent.

MM GEO-8 Slabs-On-Grade. To provide adequate support, concrete slabs-on-grade

shall bear on a minimum of 12 inches of compacted soil. The final pad

surfaces shall be rolled to provide smooth, dense surfaces upon which to

place the concrete. Slabs to receive moisture-sensitive coverings shall be

provided with a moisture vapor barrier. This barrier may consist of an

impermeable membrane. Two inches of sand over the membrane will

reduce punctures and aid in obtaining a satisfactory concrete cure. The

sand shall be moistened just prior to placing of concrete. The slabs shall be

protected from rapid and excessive moisture loss which could result in slab


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4.5-12

curling. Careful attention shall be given to slab curing procedures, as the

site area is subject to large temperature extremes, humidity, and strong

winds.

MM GEO-9 Supplemental Geotechnical Reviews. Once grading plans are generated

for the Project, these plans shall be reviewed by a geotechnical engineer.

Any additional design recommendations shall be incorporated thereafter.

MM GEO-10 Construction Monitoring. During construction, sufficient and timely

geotechnical observation and testing shall be provided to correlate the

findings of this study and the previous subsurface investigation with the

actual subsurface conditions exposed. Items requiring observation and

testing include, but are not necessarily limited to, the following:

1. Site preparation-stripping and removals.

2. Excavations, including approval of the bottom of excavations prior to

filling.

3. Scarifying and recompacting prior to fill placement.

4. Subgrade preparation for pavements and slabs-on-grade.

5. Placement of engineered compacted fill and backfill, including

approval of fill materials and the performance of sufficient density tests

to evaluate the degree of compaction being achieved.

6. Foundation excavations.

Threshold: Would the Project result in substantial soil erosion or the loss of topsoil?

Impact 4.5-2 Implementation of the Project would not result in substantial soil

erosion or the loss of topsoil. This impact would be less than

significant with mitigation incorporated.

Construction required for implementation of the Project must comply with the General

Construction Permit, which requires preparation of a Stormwater Pollution Prevention


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4.5-13

Plan (SWPPP) for the Project that lists Best Management Practices (BMPs) to be used by

the discharger during construction. Additionally, implementation of Mitigation

Measures GEO-11 and GEO-12 would ensure that substantial soil erosion does not

occur. Therefore, a less than significant impact would occur.

Upon completion of Project construction, the majority of the Project site’s surfaces

would be stabilized by landscaping or hardscaping (trails, parking lots, roads, etc.).

Because these surfaces would be stabilized, they would not be subject to substantial soil

erosion or the loss of topsoil from the Project site. Impacts would be less than significant

with mitigation incorporated.

MM GEO-11 Slope Construction. Preliminary data indicates that cut and fill slopes

shall be constructed no steeper than two horizontal to one vertical. Fill

slopes shall be overfilled during construction and then cut back to expose

fully compacted soil. A suitable alternative would be to compact the slopes

during construction, then roll the final slopes to provide dense, erosion-

resistant surfaces.

MM GEO-12 Slope Protection. Since the native materials are susceptible to erosion by

running water, measures shall be provided to prevent surface water from

flowing over slope faces. Slopes at the project shall be planted with a deep

rooted ground cover as soon as possible after completion. The use of

succulent ground covers such as ice plant or sedum is not recommended.

If watering is necessary to sustain plant growth on slopes, then the

watering operation shall be monitored to assure proper operation of the

irrigation system and to prevent over watering.


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Threshold: Would the Project be located on a geologic unit or soil that is unstable, or

that would become unstable as a result of the project, and potentially

result in onsite or offsite landslide, lateral spreading, subsidence,

liquefaction, or collapse?

Impact 4.5-3 The Project site is not located on a geologic unit or soil that is

unstable, or that would become unstable as a result of the Project

and potentially result in onsite or offsite landslide, lateral

spreading, subsidence, liquefaction, or collapse. This impact

would be less than significant.

The site lies on a relatively flat surface. The occurrence of mass movement failures, such

as landslides, rockfalls, or debris flows within such areas is generally not considered

common and no evidence of mass movement was observed on the site during the

geotechnical evaluation. The Project site is underlain by relatively dense/stiff deposits of

older alluvium soils and these materials are less susceptible to liquefaction and

settlement. In addition, the Inglewood Quadrangle Seismic Hazards Map prepared by

the California Division of Mines and Geology, 1991, shows the area of the site as being

located outside of the area that may be susceptible to liquefaction and settlement.

Therefore, the potential for liquefaction and settlement occurring at the site is

considered to be very low to low. Impacts would be less than significant.

Threshold: Would the Project be located on expansive soil, as defined in Table 18-1-B

of the Uniform Building Code (1994), creating substantial risks to life or

property?

Impact 4.5-4 Implementation of the Project would not be located on expansive

soil as defined in Table 18-1-B of the Uniform Building Code

(1994) that would create a substantial risk to life or property.

This impact would be less than significant.

The Project site is underlain by fill soils that were derived mainly from onsite grading

while alluvial sediments are present at depth. Because virtually all of the Project site has


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4.5-15

been modified to some extent in the past, no areas of natural ground remain exposed at

the surface. Existing fill thicknesses across the Project site range from less than one foot

to an anticipated maximum thickness of about 10 to 15 feet. The onsite soils consist

mainly of fine-grained clayey sand to sandy clay soils that are soft to very firm and have

low expansion potential. Therefore, impacts would be less than significant.

CUMULATIVE IMPACTS

The redevelopment of the existing EMJ Park along with new development into areas of

the Project site would not have significant cumulative impacts on the Project site or the

surrounding area. Each development project must comply with all applicable state

laws, including the CBC, and each development project must address site-specific

geology, soils, and seismicity issues to County standards through implementation of

recommendations outlined in site-specific geotechnical evaluations. Therefore, site-

specific geology, soils, and seismicity issues are addressed through compliance with

existing requirements for individual development projects, and do not contribute to a

cumulative impact regionally.


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